1. Field of the Invention
This invention pertains generally to synthesis schemes and methods for producing silicon based nanostructures and materials, and more particularly to compositions and methods for synthesis of silicon-based nanowires and composites from three-component and four-component liquid silane/polymer inks.
2. Description of Related Art
Future generation electronics will feature components that are manufactured by continuous processing. Two-dimensional webs that serve as the substrate in roll-to-roll manufacturing are subjected to additive processes where various materials are deposited and then transformed to give functioning circuit components. The beneficial electrical and electrochemical properties of silicon have been demonstrated in integrated circuits, solar cells and battery electrodes. Such materials are typically produced by chemical vapor deposition or by etching a Si wafer and these processes are not amendable to continuous manufacturing.
For example, there is increasing interest in replacing carbon-based materials with silicon or silicon-based compounds as anodes in next-generation lithium ion batteries (LIBs). Silicon has a theoretical capacity of approximately 4200 mAh/g, which is more than ten times greater than the 372 mAh/g capacity of conventional graphite anode materials. Therefore, Si-based anodes could increase the energy density of lithium ion batteries significantly.
However, fully lithiated silicon (Li22Si5) undergoes a >300% volume expansion during the lithiation and delithiation process which leads to mechanical failure of the silicon structure within a few cycles leading to a significant and permanent loss of capacity. A number of approaches toward the development of silicon-containing anodes have been attempted. One approach was the use of a homogeneous dispersion of silicon particles within a suitable matrix to give composites that have improved mechanical stability and electrical conductivity versus pure silicon. It has been shown that silicon nanowires or fibers are able to accommodate the expansion that occurs during cycling. However, significant numbers of Si-nanowires (SiNWs) are needed for practical anode applications.
A Vapor Induced Solid-Liquid-Solid (VI-SLS) route to SiNWs has been proposed that uses bulk silicon powders thus offering the possibility of scalable and cost-effective mass manufacture without the need for a localized catalyst on a substrate. The VI-SLS process, however, is complicated by high process temperatures that tend toward the formation of carbide and oxide phases that limit electrochemical capacity and rate capabilities.
Another approach to the production of silicon nanowires is through electrospinning where the electrospun polymer fiber serves only as a template for the growth of silicon coatings by hot-wire chemical vapor deposition (CVD) or plasma enhanced CVD (PECVD). While these routes do allow the growth of a-Si nanowires with hollow cores, hot-wire and PECVD suffer from poor precursor utilization and traditionally slow growth rates.
Accordingly, there is a need for an apparatus and method for reliably producing silicon based nanowires and films that are inexpensive and amenable to continuous roll-to-roll operation. The present invention satisfies these needs as well as others and is generally an improvement over the art.